Case Study Regions

The Integrated Vaal River System, west of the Lesotho Drakensberg watershed in the South African interior, is vulnerable to the occurrence of multi-year droughts. Such droughts, if intensifying in a warmer world, may potentially directly and in unprecedented ways compromise the water security of Johannesburg and the Gauteng Province, the economic hub of South Africa. Although a drought so severe that the Integrated Vaal River System can no longer supply the Gauteng Province with water (a ‘day-zero drought’) has never occurred before in the historical record, a four-year drought culminating in the El Niño drought of 2015/16 resulted in the level of the Vaal Dam falling to about 25%. A dam level below 20% would have implied the presence of a day-zero drought, since due to both engineering and water quality reasons, it would not be possible to pump water uphill to the Gauteng Province.